Re: No master_xfer_atomic for i2c-mv64xxx.c

[Chen-Yu Tsai]

On Tue, Jan 21, 2020 at 5:40 PM Maxime Ripard <mripard@xxxxxxxxxx> wrote:
>
> Hi Florian,
>
> On Sat, Jan 18, 2020 at 08:21:43PM -0800, Florian Fainelli wrote:
> > Happy new year to all of you!
>
> Happy new year to you too ;)
>
> > On a lamobo R1 (A20) the trace below can be seen by typing "halt"
> > which makes us try to perform an i2c transaction in atomic context
> > by the X-powers AXP20x driver while the i2c-mv64xxx.c driver does
> > not support it.
> >
> > I am not familiar enough with this i2c controller to suggest a way to
> > refactor it such that it would easily gain master_xfer_atomic support.
> > Is this something you could look at?
> >
> > Thanks!
> >
> > [ 1617.999014] reboot: Power down
> > [ 1618.002111] ------------[ cut here ]------------
> > [ 1618.006752] WARNING: CPU: 0 PID: 2427 at drivers/i2c/i2c-core.h:41
> > i2c_transfer+0x108/0x144
> > [ 1618.015092] No atomic I2C transfer handler for 'i2c-0'
> > [ 1618.020222] Modules linked in: pppoe ppp_async pppox ppp_generic slhc
> > crc_ccitt cmac
> > [ 1618.027987] CPU: 0 PID: 2427 Comm: procd Not tainted 5.5.0-rc5+ #0
> > [ 1618.034158] Hardware name: Allwinner sun7i (A20) Family
> > [ 1618.039376] Backtrace:
> > [ 1618.041837] [<c0238488>] (dump_backtrace) from [<c0238710>]
> > (show_stack+0x20/0x24)
> > [ 1618.049400]  r7:00000029 r6:60000093 r5:00000000 r4:c10a197c
> > [ 1618.055061] [<c02386f0>] (show_stack) from [<c096ae4c>]
> > (dump_stack+0x9c/0xb0)
> > [ 1618.062282] [<c096adb0>] (dump_stack) from [<c0252548>]
> > (__warn+0xe0/0x108)
> > [ 1618.069237]  r7:00000029 r6:00000009 r5:c075d948 r4:c0aefafc
> > [ 1618.074895] [<c0252468>] (__warn) from [<c0252944>]
> > (warn_slowpath_fmt+0x94/0x9c)
> > [ 1618.082369]  r7:c075d948 r6:00000029 r5:c0aefafc r4:c0aefbc0
> > [ 1618.088026] [<c02528b4>] (warn_slowpath_fmt) from [<c075d948>]
> > (i2c_transfer+0x108/0x144)
> > [ 1618.096195]  r8:00000032 r7:c10a93e4 r6:00000001 r5:ea32fd3c r4:ea945ca8
> > [ 1618.102892] [<c075d840>] (i2c_transfer) from [<c075d9d0>]
> > (i2c_transfer_buffer_flags+0x4c/0x5c)
> > [ 1618.111579]  r6:eb3c6501 r5:00000001 r4:00000002
> > [ 1618.116199] [<c075d984>] (i2c_transfer_buffer_flags) from
> > [<c0675658>] (regmap_i2c_write+0x24/0x40)
> > [ 1618.125229]  r4:00000002
> > [ 1618.127768] [<c0675634>] (regmap_i2c_write) from [<c06703d8>]
> > (_regmap_raw_write_impl+0x72c/0x908)
> > [ 1618.136713]  r5:00000001 r4:ea8d9c00
> > [ 1618.140291] [<c066fcac>] (_regmap_raw_write_impl) from [<c0670630>]
> > (_regmap_bus_raw_write+0x7c/0xa0)
> > [ 1618.149501]  r10:00000058 r9:ea32e000 r8:fee1dead r7:00000080
> > r6:00000032 r5:c066be98
> > [ 1618.157319]  r4:ea8d9c00
> > [ 1618.159857] [<c06705b4>] (_regmap_bus_raw_write) from [<c066fa08>]
> > (_regmap_write+0x7c/0x164)
> > [ 1618.168371]  r7:ea8d9c00 r6:00000080 r5:00000032 r4:ea8d9c00
> > [ 1618.174029] [<c066f98c>] (_regmap_write) from [<c0671294>]
> > (regmap_write+0x4c/0x6c)
> > [ 1618.181679]  r9:ea32e000 r8:fee1dead r7:0002e574 r6:00000080
> > r5:00000032 r4:ea8d9c00
> > [ 1618.189420] [<c0671248>] (regmap_write) from [<c067d0ac>]
> > (axp20x_power_off+0x3c/0x48)
> > [ 1618.197328]  r7:0002e574 r6:28121969 r5:c1004e90 r4:4321fedc
> > [ 1618.202985] [<c067d070>] (axp20x_power_off) from [<c023605c>]
> > (machine_power_off+0x34/0x38)
> > [ 1618.211332] [<c0236028>] (machine_power_off) from [<c027850c>]
> > (kernel_power_off+0x7c/0x80)
> > [ 1618.219676] [<c0278490>] (kernel_power_off) from [<c02786a0>]
> > (__do_sys_reboot+0x190/0x1f4)
> > [ 1618.228019] [<c0278510>] (__do_sys_reboot) from [<c0278774>]
> > (sys_reboot+0x18/0x1c)
> > [ 1618.235669]  r8:c0201324 r7:00000058 r6:b6f69010 r5:becbbe2c r4:00000000
> > [ 1618.242366] [<c027875c>] (sys_reboot) from [<c0201120>]
> > (ret_fast_syscall+0x0/0x4c)
> > [ 1618.250013] Exception stack(0xea32ffa8 to 0xea32fff0)
> > [ 1618.255062] ffa0:                   00000000 becbbe2c fee1dead
> > 28121969 4321fedc 0002e574
> > [ 1618.263231] ffc0: 00000000 becbbe2c b6f69010 00000058 ffffffff
> > 00000000 0000201d 00000001
> > [ 1618.271398] ffe0: 0002de54 becbbd5c 0001ac8c b6f8e408
> > [ 1618.276443] ---[ end trace 526da779414c6638 ]---
>
> Is that on every reboot?
>
> However, I'm not entirely sure how we could implement it without
> sleeping. The controller is basically a state machine that triggers an
> interrupt on each state change, so you first set the address, get an
> interrupt, then set the direction, then you get an interrupt, etc.
>
> I guess we could implement it using polling, but I'm not sure if
> that's wise in an interrupt context either.

I believe that is actually how some of the other drivers handle it,
using polling. You can mask or disable the interrupts while in the
xfer_atomic callback, and the i2c core won't schedule two transfers
at the same time anyway.

ChenYu